WASHINGTON The U.S. Congress approved $750 million in aid last December to help El Salvador, Guatemala and Honduras combat the violence and poverty that are driving migrants towards the U.S. border, but the money has yet to reach the struggling countries.

In a departure from previous aid packages, the State Department first had to certify that the three nations had taken steps to reduce migration and human trafficking, bolster human rights and improve their justice systems.

Eight months after President Barack Obama signed a spending bill that included the funds, congressional aides told Reuters they were still waiting for the State Department certifications needed to release the money, which was budgeted for the fiscal year ending Sept. 30.

State has not provided its paperwork and Central American governments have not taken the required actions, congressional aides said. Lawmakers have been particularly unhappy about Honduras because of the murder of a prominent environmental activist there.

"The fiscal year 2016 funds have not been obligated because the State Department has not yet submitted a detailed plan as required by law, spelling out how, where and by whom the funds will be used, what their objectives are and how they will measure progress," said Tim Rieser, a foreign policy aide to Senator Patrick Leahy, the top Democrat on the Senate subcommittee that oversees foreign aid.

The delay highlights the longstanding tension between Washington's desire to promote human rights and the government's responsibility to protect U.S. security, economic and other interests. In this case, American lawmakers are reluctant to send hundreds of millions of dollars to countries where human rights abuses remain common, despite the flood of migrants towards the U.S. border.

They want to avoid a repeat of past aid programs, in which large amounts of money sent south yielded few results.

"The results have been very disappointing. Programs were poorly conceived, the Central American governments did not do their part, and money was wasted," Rieser said.

From October 2015 through January 2016, U.S. border patrols stopped some 45,000 Central Americans in the U.S. southwest, more than double the number during the same period a year earlier. Nearly half were unaccompanied children.

None of the countries has yet to meet all the conditions, congressional aides said, although Guatemala is further along. Honduras faces harsh criticism about human rights from lawmakers, due in part to the killing of internationally acclaimed environmentalist Berta Caceres in March.

Dozens of lawmakers have demanded an independent international investigation into her death, and Honduran authorities have arrested five suspects, including an Army officer and an employee of a company running a dam project she opposed.

A spokesman said the State Department was working to obtain congressional approval for the fiscal 2016 funds. In the meantime, he said, the department and U.S. Agency for International Development are using money from prior years to support the U.S. "Strategy for Engagement in Central America."Guatemalan officials told Reuters they expected their funds to begin arriving between October and November.

In Tegucigalpa, a foreign ministry official who requested anonymity said Honduras has made progress fighting corruption and combating smuggling and hoped the funds would start being released later this year or early in 2017.

In San Salvador, a foreign ministry official said the government was awaiting word on the disbursement, also saying the government had made progress.

Separately, the Obama administration late last month announced the expansion of a programme to let people fleeing violence in the three countries enter the United States as refugees, and said Costa Rica agreed to shelter some of them temporarily.

(Additional reporting by Enrique Pretel in San Jose, Nelson Renteria in San Salvador and Gustavo Palencia in Tegucigalpa; editing by John Walcott and David Gregorio)

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